Rotating bands are used on projectiles fired from barrels in order to give both a gas seal between the projectile and the barrel and a good friction coupling against the barrel. Traditionally, projectiles are rotationally stabilized in order to acquire better aerodynamic properties, by virtue of the projectile being made to rotate during the launch process as the result of a rifling made in the barrel. When the projectile provided with a rotating band is driven out of the barrel, the rotating band is partially deformed by the rifling and thus the rotating band grips the rifling and rotates the projectile with the pitch belonging to the rifling. Should a guidable projectile be desired, it is expedient for the projectile to be roll-stable, that is to say non-rotating, when fins are deployed and in use. Since it is desirable to use the same barrel, and thus launcher, for all projectiles, the guidable projectiles are constructed with a slipping rotating band and can thus be launched from a rifled barrel. The slipping rotating band of the guidable projectile will grip the rifling in the barrel and create a gas seal. When the projectile is propelled in the barrel, the rotating band will rotate with the pitch of the rifling. The coupling between the rotating band and the projectile is constructed such that the friction is low and slipping or sliding against the projectile occurs, which means that the projectile does not rotate or rotates with a significantly lesser rotation than in the case of a fixedly mounted rotating band. When the projectile leaves the barrel, the rotation of the projectile will be low. Apart from the fact that it is advantageous for guidable projectiles to be roll-stable, a low rotation in the barrel is important in order to reduce the forces which are generated by the angular acceleration and to which the electronics and mechanics mounted in the projectile are subjected at launch.
U.S. Pat. No. 4,552,071 A, for example, discloses an invention which shows a slipping rotating band consisting of two concentric parts, firstly an outer ring, referred to as a wiper, and secondly an inner ring, in which the part referred to as a wiper is made of a soft material, for example nylon-6. The rotating band is designed, however, not to remain permanently in place after the projectile has left the barrel.
An example of another previously known invention can be found in U.S. Pat. No. 6,453,821 B1, which shows a rotating band for handling high temperatures. The description in the patent text refers to a number of alternative materials, for example in the form of a composite. A projectile is provided with a groove made, in principle, in the middle of the projectile, which is especially suitable for long projectiles. A rotating band is mounted in the groove and configured with notches on the outer radius of the rotating band. The rotating band is not permanent, but will be broken into parts after the projectile has left the barrel. Once the rotating band has been accelerated to the same speed as the projectile, then the rotating band or parts of the rotating band will, per se, become one or more projectiles and give rise to an increased risk for persons and equipment in the surrounds of the launcher.
Permanent and fixedly mounted rotating bands are usually found on rotationally stabilized ammunition and are then often made of a softer metal, for example copper. These rotating bands are not slipping, since a good contact between the rotating band and the projectile is necessary to obtain high rotation of the projectile and thus also good rotational stability of the projectile in the path between the launcher and the target. Permanent and fixedly mounted rotating bands cannot therefore be used for roll-stable guidable projectiles.